The construction of mobile vehicles, such as caravans, motor-homes, box vans, etc., has changed little in the past few decades. Typically, the mobile vehicle has a body shell constructed from large composite panels, which form the front, back, sides and roof of the vehicle. With existing construction techniques, the panels are directly screwed together at their panel edges and the screw holes and seam are then sealed by covering the joint area with a narrow strip of material, or an extrusion such as an Aluminium “awning rail”. Providing this seal to a consistent and acceptable cosmetic standard can be difficult to achieve by the existing construction techniques. It is also labour intensive and generates much wasted material. Moreover, the structural rigidity of the assembled panels is reliant on the consistency of the panel materials that are being screwed together and the skill of the operator.